Project Summary/Abstract The goal of this project is to define the role of inflammation in the pathogenesis of arrhythmogenic cardiomyopathy (ACM), a familial non-ischemic heart muscle disease that causes sudden death in the young and especially in athletes. Exercise accelerates disease penetrance, and increases arrhythmic risk and adverse cardiac events in ACM patients, but how exercise exacts this terrible toll is not known. We now report substantial new data showing that ACM disease alleles activate NF?B signaling in cardiac myocytes and that inhibition of this signaling pathway prevents the full ACM disease phenotype in a robust, well characterized mouse model. We also show that exercise greatly intensifies inflammatory signaling, thus providing a new mechanistic explanation for accelerated disease progression in athletes. These observations suggest that targeted anti-inflammatory therapy could be a powerful, truly mechanism-based approach to reduce adverse events in ACM patients. Accordingly, we will test the hypotheses that 1) activation of an innate immune response in cardiac myocytes mediated by NF?B causes arrhythmias and myocardial damage in ACM; and 2) exercise accelerates progression of ACM by stimulating production of injurious inflammatory mediators via activation of NF?B signaling in cardiac myocytes. In Aim 1, we will use genetic approaches in defined mouse models to elucidate the relative contributions to the ACM disease phenotype of activation of an immune response in cardiac myocytes vs. the actions of infiltrating inflammatory cells. In Aim 2, we will characterize effects of exercise on inflammation in ACM and define new mechanisms by which exercise promotes myocardial injury and arrhythmias. And in Aim 3, we will test the efficacy of selected FDA-approved drugs to prevent clinically important features of the ACM disease phenotype and mitigate the dangerous effects of exercise. We will also characterize expression of miRNAs that regulate NF?B and GSK3? signaling to identify RNA-based strategies to turn off inflammatory signaling. Such preclinical testing, we hope, will provide a pathway to future clinical trials in patients with ACM.